The present invention relates to an optical reading apparatus having a shading plate for reducing the difference in amount between the light passing through the central portion of a focusing lens and the light passing through the peripheral portion of the lens.
FIG. 1 schematically shows a facsimile device 1, a typical device in which an optical reading apparatus is used. As is shown in this figure, facsimile device 1 comprises sheet table 3, feed rollers 4 reading section 14 (including lamp 5, lens 6, and reading apparatus 7), sheet-transporting path 8, sheet stacker 9, printer 11, paper-receiving table 12, receiver 14, and feed rollers 15. A roll of recording paper 10 is set in a housing of facsimile device 1.
In operation, sheet 2 (i.e., an original) is placed on table 3. Feed rollers 4 which contact each other, are rotated, thereby feeding sheet 2 from table 3 into the housing of device 1. Lamp 5 is turned on, thus applying light to that side of sheet 2 on which a pattern image is formed. The light reflected from this side of sheet 2 is supplied through lens 6 to reading apparatus 7. Thus, the reading section 14 reads the pattern image from sheet 2, and converts the image into electric signals.
The electric signals, or facsimile signals, are transmitted from a transmitter (not shown) provided within the housing, to a receiving facsimile device which is identical in structure with facsimile device 1. After sheet 2 has been exposed to the light emitted from lamp 5, it is fed by feed rollers 4 and transported through path 8 into sheet stacker 9.
Receiver 14 of the receiving facsimile device receives the facsimile signals sent from device 1. The signals are supplied to printer 11. Printer 11 converts the signals into a pattern image, and prints this image on recording paper 10 fed out of the roll. That part of paper 10 on which the image has been printed is cut and fed by feed rollers 15.
Reading apparatus 7 will be described in detail, with reference to FIG. 2. As is illustrated in FIG. 2, apparatus 7 comprises shading plate 21 and base 22. Plate 21 is fastened to base 22 by means of screw 24, with a leaf spring 23 interposed between plate 21 and base 22. When screw 24 is turned in either direction, shading plate 21 is moved in the direction of arrow A, that is, in the direction perpendicular to light path 25 of the reading apparatus 7. Apparatus 7 further comprises mirrors 26 and 27, lens mount 28, sensor 29, and lens 30. Lens mount 28 is set on base 22 and holds lens 30. Sensor 29 is located at the rear of lens mount 28.
The light emitted from lamp 6 is applied to sheet 2 (i.e., an original) on which a pattern image is formed. The light is reflected from sheet 2, and is supplied to mirror 26. Mirror 26 reflects the light and applies it to mirror 27. Mirror 27 reflects the light and applies it to lens 30 in light path 25. Lens 30 focuses the light, thereby projecting the pattern image onto the light-receiving surface of sensor 29.
Another conventional reading apparatus will be described, with reference to FIG. 3. As is shown in FIG. 3, this reading apparatus comprises shading plate 31, lens mount 28, screw 32, sensor 29, and lens 30. The shading plate 31 is directly attached to lens mount 28 by screw 32 which passes through an elongated hole made in shading plate 31. The axis of the elongated hole extends perpendicular to light path 25 of the reading section. To adjust the position of shading plate 31, screw 32 is turned in one direction and is thus loosened. Then, plate 31 is moved in the direction of arrow B, that is, in the direction perpendicular to light path 25. Finally, screw 32 is turned in the opposite direction, thus fastening plate 31 to lens mount 28. As a result, plate 33 is fixed at an optimum position. The light reflected from the sheet (not shown) is applied in path 25 to lens 30. Lens 30 focuses the light, thereby projecting the pattern image, which is formed on the sheet, onto the light-receiving surface of sensor 29.
In the reading section shown in FIG. 2, shading plate 1 is attached to base 22 by screw 24, with leaf spring 23 interposed between plate 21 and base 22. Due to the force which spring 23 exerts on screw 24, screw 24 is likely to turn loose. To secure screw 24, thereby to prevent the loosening of screw 24, a nut must be used. However, the use of the nut not only increases the number of parts forming the reading section, but also renders it difficult to adjust the position of shading plate 21.
In the reading apparatus illustrated in FIG. 3, shading plate 21 is attached to the front of lens mount 28 by screw 32 which passes through the elongated hole of plate 31. Hence, to adjust the position of plate 31, a screw driver must be positioned in front of the reading section, it is difficult to use a screw driver thus positioned. Consequently, it is difficult and time-consuming to adjust acutely the position of plate 31.
Either known reading section is considered disadvantageous in the following respect. Since the shading plate is moved perpendicular to the light path and toward the light path, thereby to reduce the amount of the light passing through the central portion of the lens, the amount of light passing through the peripheral portion of the lens is inevitably reduced, though it should not be reduced.
More specifically, FIGS. 4(a) and 4(b) show different positional relationships between the shading plate (21, 31) and the lens 30. As is evident from these figures, when the shading plate is moved toward the axis of the light path, that is, from the position shown in FIG. 4(a) to the position shown in FIG. 4(b), in order to reduce the amonut of light incident on the lens, it will cover a greater peripheral portion of the lens. Obviously, the closer the plate is to the axis of the light path, the lens light will pass through the peripheral portion of the lens.
FIG. 5 is a graph showing the characteristics of the shading achieved in the conventional reading apparatus. It represents the light distribution in percentage along the diameter of the lens (which corresponds to the width of sheet 2, i.e., the original). The distance from the center of the lens is plotted on the X axis, whereas the percentage of light is plotted on the Y axis. The amount of the light, which is applied to the center of the lens when the shading plate is outside the optical path (5, 16), is rated as maximum, i.e., 100%.
Curve C.sub.0 shown in FIG. 5 represents the distribution of light which is applied to the lens when no shading is performed. Curves c.sub.1, C.sub.2, C.sub.3, and C.sub.4 indicate how the distribution of light changes as the shading plate (21, 31) is moved deeper into the light path 25. As these curves demonstrate, when the light incident on the center portion of the lens is reduced, the light incident on the periphery portion of the lens is also reduced.